The present invention relates to a transfer device employing a hollow roller as a roller for entraining a transfer belt, as well as an image forming apparatus incorporating such a transfer device.
An electrophotographic image forming apparatus uses a transfer device for transferring a developer image born on a surface of a photoreceptor to a recording sheet. Since the transfer device is in contact with the photoreceptor during printing, the transfer device has to be moved so as to separate from the photoreceptor when a sheet jam occurs. In order to reduce the weight of the whole transfer device, consideration is given to use of a hollow roller as a roller entraining the transfer belt.
However, the use of such a hollow roller for entraining the raises a problem that a required strength for entraining the transfer belt cannot be obtained.
In attempt to solve this problem, a transfer device has been disclosed which includes a hollow roller formed with a plurality of ribs extending from a bearing of the hollow roller toward the inner periphery of the roller (see Japanese Patent Laid-Open Publication No. 2004-138813 for example).
The transfer belt used in the transfer device is a member comprising elastic rubber and formed with meandering preventive ribs which are provided at opposite edges of the belt on the side in contact with the roller and which project in a direction perpendicular to the longitudinal direction of the roller. The ribs of the hollow roller disclosed in Japanese Patent Laid-Open Publication No. 2004-138813 have longitudinal end faces located coplanar with an end face of the hollow roller.
Therefore, in cases where the hollow roller disclosed in Japanese Patent Laid-Open Publication No. 2004-138813 is used as a roller for entraining the transfer belt of the transfer device, the meandering preventive ribs of the transfer belt come into contact with the rib edges of the hollow roller, thereby raising problems that: the meandering preventive ribs are shaved; and meandering preventive ribs run on the hollow roller. This is because the edges of concern come into contact with the meandering preventive ribs so as to resist the moving track of the meandering preventive ribs.
When rubber debris resulting from shaving of the meandering preventive ribs is scattered inwardly of the transfer belt, an uneven transfer nip occurs, which causes a poor image quality to result. When the rubber debris is scattered in a cleaning blade nip associated with the photoreceptor, a cleaning failure is caused to occur. When the meandering preventive ribs of the transfer belt run on the hollow roller, problems arise that: the transfer belt broken; and the transfer device body becomes faulty.
In view of the foregoing problems, a feature of the present invention is to provide a transfer device capable of preventing the ribs of the hollow roller from shaving the meandering preventive ribs which are formed on the transfer belt for preventing the transfer belt from meandering while preventing the meandering preventive ribs from running on the hollow roller.